Technical Field
The present invention relates to a voltage sensor abnormality diagnosis apparatus.
Related Art
Conventionally, apparatuses are known which diagnose an abnormality of a voltage sensor in a system converting DC voltage of a battery to AC voltage by using an inverter to supply the AC voltage to an AC motor.
For example, the fault diagnosis apparatus for voltage sensors disclosed in Japanese Patent No.4793058 determines that any of the voltage sensors has failed if the absolute value of the difference between a battery voltage VBf detected by a battery voltage sensor and an inverter voltage VIf detected by an inverter voltage sensor is larger than a predetermined value.
In addition, the fault diagnosis apparatus compares a first output estimated value, which is the three-phase sum of products of phase currents and phase voltages of individual phases, with a second output estimated value, which is calculated based on the product of torque and the number of revolutions of a motor. If the absolute value of the difference between the output estimated values is larger than a predetermined value, the fault diagnosis apparatus determines that the inverter voltage sensor has failed.
According to the technique in Japanese Patent No.4793058, two output estimated values are compared with each other, and voltage values are not directly evaluated. If a determination threshold value is set to be constant regardless of voltage values, the degree of the range, which is the determination threshold value or less and in which it is determined to be normal, varies depending on the voltage values. Hence, it is difficult to secure uniform accuracy in determining an abnormality in a wide voltage region. In addition, variably setting the determination threshold value depending on the voltage value increases a calculation load.
Furthermore, in a system in which output voltage of a battery is directly inputted to an inverter, the battery voltage and the inverter input voltage are approximately equal to each other when wiring loss is ignored. Hence, both of the battery voltage sensor and the inverter input voltage sensor are not required to be provided. However, according to the technique in Japanese Patent No.4793058, the battery voltage sensor is required to be provided only for detecting an abnormality of the inverter voltage sensor and to obtain a battery voltage signal from a vehicle controller by a voltage sensor diagnosis section of a motor controller.